1. Field of the Invention
This invention relates to a method by which a surface-emitting semiconductor device suited for two-dimensional array structure can be fabricated simply and at a high yield, a surface-emitting semiconductor device fabricated by such a method, and a display device making use of such a device.
2. Related Background Art
In recent years, two-dimensional array type surface solid-state light-emitting devices are sought to be developed so that they can be applied to large-capacity parallel light information processing, high-speed optical couplers and thin-type display devices. In order for the former to be applied to the latter, the devices are required to be inexpensive, to have a low power consumption, to have a high productivity and to have a high reliability. Materials for the surface solid-state light-emitting devices have been studied and developed in variety, and semiconductor single crystals are very suited for ensuring reliability. In particular, surface-emitting semiconductor devices making use of compound semiconductors are being developed energetically. Compound semiconductors make it possible to emit light over a wide-range wave band of from ultraviolet to infrared by changing materials for substrates and laminate structures, and are considered promising as display devices. Also, among light-emitting devices, laser diodes (LD) having light reflectors on both ends have very high light-emitting efficiency compared with natural light emission, and hence can make power consumption small even when formed in two-dimensional array. From such a viewpoint, Vertical Cavity Surface Emitting Laser (VCSEL) is actively developed in recent years.
At present, such VCSELs are also being developed first on those emitting blue light of wavelength of about 400 nm and up to those emitting light of 1.55 .mu.m which is at a communication wave band. Researches are made on materials of, e.g., an AlGaN/InGaN system on a sapphire substrate, an InGaAlP/InAlP or InGaAs/AlGaAs system on a GaAs substrate and a InGaAs/InGaAsP system on an InP substrate.
A basic structure of a prior art VCSEL is shown in FIG. 1. It has a structure wherein laser light is vertically emitted through a substrate 201 and 99% or more highly reflective films 209 are provided on both sides of an epitaxially grown layer of several .mu.m thick. In FIG. 1, reference numeral 202 denotes an etching stop layer; 203 and 205, clad layers; 204, an active layer; 206, a contact layer; 207, an insulating layer; 208, electrodes; and 210, a buried layer.
As the reflective films, multiple layers formed of .lambda./4-thick films having different refractive indexes are chiefly used. As materials therefor, dielectrics as in the example shown in FIG. 1 or epitaxially grown semiconductors are commonly used. Examples of epitaxially grown mirrors include those in which an AlAs/GaAs multi-layer film mirror, an active layer and so forth are formed on a GaAs substrate by one-time growth as disclosed in ELECTRONICS LETTERS, 31, p.560 (1995), and those in which a GaAs/AlAs mirror formed on a GaAs substrate is bonded by direct joining to a laser structure of an InGaAsP/InP system grown on an InP substrate as disclosed in APPLIED PHYSICS LETTER, 66, p.1030 (1995).
However, in the case where semiconductor epitaxial layers are used as the multi-layer film mirror, the refractive indexes can not be made so much different that many layers must be formed, which take a long growth time and give a large layer thickness, and hence a low productivity may result and the films can be worked or smoothed with difficulty. Also, in such semiconductor mirrors, a practical material is GaAs/AlAs under the existing conditions, which, however, taking account of lattice constant, may impose limitations on materials usable for the active layer, resulting in limitations on oscillation wave bands. In the case where the GaAs/AlAs mirror is bonded by direct joining, materials usable for the active layer can be selected from a broader range and the films can also be applied to other wave bands. There, however, are limitations on the size of the semiconductor substrate, and hence this method can be effective only for small-area ones.
On the other hand, the dielectric multi-layer film a=: mirror can be produced simply, but can not be formed on the substrate as it is. Hence, the films must be formed after the back of the substrate 201 is etched to make a window 201a as shown in FIG. 1, where the window is required to be formed with precision and also windows can not be made so much close to each other. Thus, the yield and uniformity are so poor that the device can not be formed in a high density, and hence there has been a problem when formed in two-dimensional array.
Meanwhile, Japanese Patent Application Laid-open No. 9-223848 discloses a method comprising epitaxially growing on a semiconductor substrate, semiconductor layers having a semiconductor active layer, bonding this semiconductor substrate to an integrated-circuit substrate, and thereafter removing the semiconductor substrate to fabricate a semiconductor device on which a surface-emitting semiconductor device and other electrical devices are integrated. A schematic cross-sectional view of this semiconductor device is shown in FIG. 2. In FIG. 2, reference numeral 500 denotes a light input-output substrate; 500A, light-receiving elements; 500B, vertical oscillator type surface-emitting lasers; 500C and 500D are each wiring for the light-receiving elements 500A and surface-emitting lasers 500B; 200, an integrated-circuit substrate; 200A, metal wiring of the integrated-circuit substrate 200; 300, an insulating layer; 400, wiring; L.sub.c, output light; and L.sub.i, an input light.
The semiconductor device shown in FIG. 2, however, is not a device making use of a substrate comprised of light-transmitting material so that the light is emitted from the substrate side. Also, the semiconductor device shown in FIG. 2 is provided with wiring at terraced portions at each light-emitting area, and hence has had a problem that it is difficult to form the wiring to bring about a poor yield. Especially when the dielectric multi-layer film mirror is fabricated on the semiconductor layer under the constitution shown in FIG. 2, a remarkably low yield may result.